"South Korea, Japan and Taiwan have all refrained from developing nuclear arsenals because they enjoy the military protection of the United States.

However, the growing military and economic power of China, the threat posed by North Korea and weakening ties with Washington since the end of the Cold War are causing the three US allies to question their security.

A US announcement last month of plans to reduce its number of troops in Asia by about 20,000 in the next 10 years has increased doubts about US commitment to defend its allies."